This invention relates to concentrated water-in-oil emulsions of water-soluble polymers wherein the emulsions can be inverted into a continuous aqueous phase. This invention also relates to processes for preparing such emulsions.
Various water-soluble polymers such as polyacrylamide and copolymers of acrylamide with other monomers are well-known to be precipitants or flocculants for many substrates including sewage, cellulosic fibers and fines for retention and freeness, effluent waste for metal production, coal tailings and the like. Such polymers are also known to exhibit superior thickening properties when said polymers are dissolved in aqueous media. Particularly well-known for this purpose are the anionic polyacrylamides such as acrylamide/acrylic acid copolymers, including those prepared by hydrolysis of polyacrylamide. Such polymers are also very useful as fluid mobility control agents in enhanced oil recovery processes.
In the past, such polymers have been made available commercially as powders or finely divided solids which must be subsequently dissolved in an aqueous medium in order to be used. Because such dissolution steps are sometimes time consuming and often require rather expensive mixing equipment, it has become a common practice to formulate the water-soluble polymers in water-in-oil emulsions wherein the polymer is dissolved in the dispersed aqueous phase. Such emulsions, as well as methods for preparing them, are described in U.S. Pat. No. 3,284,393 to Vanderhoff et al. Unfortunately, for many applications, these emulsions do not invert as readily as desired. In order to accelerate the inversion rate of such emulsions, it has been a common practice, e.g., as shown in U.S. Pat. No. Re. 28,474, to add a water-soluble surfactant to the emulsion during or just prior to inversion. While the foregoing procedures generally do overcome the problems of dissolving dry powders of water-soluble polymers in aqueous media, such emulsions contain substantial quantities of water and oil, thus increasing the cost of shipping and handling such polymers to a significant degree.
In an attempt to overcome the latter problem, it is taught in U.S. Pat. No. 4,052,353 to concentrate such emulsions by removing water from the emulsions and subsequently adding sufficient water-soluble surfactant to render the water-soluble polymer self-dissolving in water. Unfortunately, however, the stability of such dispersions after storage for significant periods is not as much as desired.
In view of the foregoing deficiencies of conventional emulsions and concentrated dispersions derived from such emulsions, it is highly desirable to provide a concentrated water-in-oil emulsion of a water-soluble polymer that can be inverted quickly into an aqueous medium but can be stored for substantial periods of time without losing such ability to be inverted.